1. Field of the Invention
The present invention relates to display devices, electronic devices, and driving methods thereof, and particularly to a display device using especially current-driven luminescence elements, an electronic device, and driving methods thereof.
2. Description of the Related Art
Image display devices (organic EL displays) using organic light emitting diodes (OLEDS) are known as image display devices using current-driven luminescence elements. The organic EL displays have advantages such as viewing angle properties and low power consumption, and thus have attracted attention as next-generation flat panel display (FPD) candidates.
In a usual organic EL display, organic EL elements serving as pixels are arranged in a matrix. An organic EL display is called a passive-matrix organic EL display, in which organic EL elements are provided at intersections of row electrodes (scanning lines) and column electrodes (data lines) and voltages corresponding to data signals are applied to between selected row electrodes and the column electrodes to drive the organic EL elements.
On the other hand, an organic EL display is called an active-matrix organic EL display, in which thin-film transistors (TFTs) are provided at intersections of scanning lines and data lines, connected to gates of driving transistors, and turned on through selected scanning lines, and then data signals are inputted to the driving transistors via signal lines.
Unlike the passive-matrix organic EL display in which organic EL elements connected to each of the row electrodes (scanning lines) produce luminescence only in a period during which each row electrode is being selected, a decrease in luminance of a display is not caused even when a duty ratio increases, because the active-matrix organic EL display allows the organic EL elements to produce luminescence until next scanning (selection). Thus, the active-matrix organic EL display can be driven at a low voltage, thereby achieving less power consumption. However, the active-matrix organic EL display has a disadvantage that, even when the same data signals are provided, each of pixels has different luminance of organic EL element due to characteristic variation of a driving transistor or an organic EL element, and luminance unevenness occurs.
For a conventional organic EL display, for instance, a compensation using complex pixel circuits, a feedback compensation using representative pixels, and a feedback compensation using a sum of currents flowing in all pixels are representative as a compensation method for luminance unevenness caused by characteristic variation or deterioration of a driving transistor or an organic EL element (hereinafter, collectively referred to as uneven characteristic).
However, the complex pixel circuits reduce yield. In addition, the feedback using the representative pixels and the feedback using the sum of currents flowing in all the pixels do not make it possible to compensate the uneven characteristic for each pixel.
For the above reasons, methods for use in simple pixel circuits which detect an uneven characteristic for each pixel have been proposed.
For example, in a substrate for luminescence panel, a test method thereof, and a luminescence panel disclosed in Patent Reference 1 (Japanese Unexamined Patent Application Publication No. 2006-139079), a voltage driving pixel circuit including two conventional transistors is connected to a transistor as a diode, a current flowing into a test line connected to the transistor connected as the diode is measured in a substrate for luminescence panel before EL formation, with the transistor being regarded as an EL element, a relationship between a data voltage and a current flowing into a driving transistor is detected, and pixel test and pixel characteristic extraction are performed. Furthermore, the transistor connected as the diode makes it possible to prevent a current from flowing as a reverse bias, using the test line, after the EL formation, and thus a normal voltage writing operation can be performed. Moreover, a characteristic detected for each pixel can be used for correction control of an applied voltage to a data line at the time of using an organic EL luminescence panel.